1. Field of the Invention
The present invention relates generally to a guide device configured to guide, in a predetermined direction, a sheet positioned on a tray. In particular, the present invention is directed towards a guide device comprising a pair of side guides configured to reliably guide the sheet in the predetermined direction when the sheet is fed.
2. Description of Related Art
Known image processing apparatus, such as copying machines and printers, may include a tray that is configured to receive and to hold a plurality of sheets, such as a plurality of documents or recording sheets. The sheets positioned on the tray are separated one by one and are fed to a position at which the sheet may be scanned, or to a position at which an image may be recorded on the sheet. The tray may include at least one side guide configured to guide the sheets in a sheet feeding direction. The side guide includes an elongated plate having a plane, i.e., a guide surface, extending along the sheet feeding direction. The side guide includes a side registration type and a center registration type. A side guide of the side registration type may be configured to movable in a direction toward and away from a fixed reference plane with which a side edge of a sheet is to contact. The side guide is disposed, such that a guide surface thereof and the fixed reference plane face each other. An opposite side edge of the sheet is to contact the guide surface of the side guide. A pair of side guides of the center registration type are configured to be movable in a direction relative to each other. The side guides are disposed, such that their guide surfaces face each other. Side edges of a sheet are to contact the respective guide surfaces of the side guides. The side guides of both of the types are configured to be slidable in a direction perpendicular to the sheet feeding direction to adjust a distance between the side guide and the fixed reference plane, or a distance between the side guides in accordance with a width of the sheet positioned on the tray. With the side guides of the either of the types, skewing of the sheet during the sheet feeding may be minimized.
A rack-and-pinion interlock mechanism is known to be used to slide the pair of side guides of the center registration type. The known interlock mechanism includes two racks and a pinion. The racks extend from the respective side guides in a direction perpendicular to the sheet feeding direction. The pinion is configured to engage both of the racks. The tray includes a groove in which the racks are movable. The groove is defined by walls on which the racks are slidable. The tray further includes a fixing portion to fix the pinion rotatably. With this structure, when one of the side guides slides, the pinion rotates in response to a linear motion of the rack for the sliding side guide, such that the rotational force of the pinion is transferred to the other rack. Consequently, the other side guide slides in synchronization with the sliding of the one side rack.
In the known side guides, a clearance may be positioned between a slide support portion, e.g., the groove or the wall and the rack, or between each of the racks and the pinion in order to ensure the operability of the side guides. Therefore, the sliding motion of the side guides becomes smoother, such that the side guides readily may slide.
Nevertheless, the clearance between the slide support portion and the rack, or the clearance between each of the racks and the pinion, may be a factor in rattling the side guides. If the side guides rattle, the side guides may be tilted with respect to the sheet feeding direction. If the side guides are tilted, a sheet positioned between the side guides is conveyed and skewed with respect to the sheet feeding direction. When a relatively larger standard-size sheet, for example, an A4-size sheet, a B5-size sheet, or a sheet larger than those size sheets, is fed, a distance between each of the side guides and the pinion increases. At that time, a distance between a first contact portion, which may be positioned at one end of the rack and is to contact the wall of the groove, and a second contact portion, which may be positioned at the other end of the rack and is in contact with the pinion, decreases. When a relatively smaller standard-size sheet, for example, a postcard or a standard photo sheet, is fed, the distance between each of the side guides and the pinion decreases. At that time, the distance between the first contact portion and the second contact portion increases. In any of these cases, a distance between the wall of the groove and a portion of the rack opposite to the first contact portion thereof is substantially the same. Nevertheless, the degree of ratting of the side guides may vary in accordance with the size of a sheet to be fed. That is, the variation in the degree of ratting of the side guides occurs because the distance between the first contact portion and the second contact portion varies in accordance with the size of a sheet to be fed. The rattling of the side guides may be reduced when a relatively larger sheet is fed. The ratting of the side guides may be increased when a relatively smaller sheet is fed, such that the skewing of the sheet is more likely to occur. The skewing of the sheet is undesirable because it may cause fluctuations in a read image, or may cause displacement of an image to be recoded on the recording sheet.
If the clearance between the slide support portion and the rack, or the clearance between each of the racks and the pinion, is decreases, the rattling of the side guides may decrease, such that the degree of the skewing of the sheet may be reduced. Nevertheless, the operability of the side guides also may decrease due to the increased sliding resistance of the slide support portion, or due the increased resistance caused by the engagement of the racks and the pinion.